Introduction - Microwave-Assisted Concrete Technology: Production, Demolition and Recycling - page 6

1.2.2 Microwave- assisted selective
demolition and drilling of concrete
Demolition and drilling of concrete using conventional techniques generate
considerable noise and a lot of dust. Moreover, a major problem associated
with the current state-of-the-art concrete demolition techniques is the lack
of selectivity. Because of concrete toughness, it is difficult to demolish or
drill into one part of a concrete component without affecting the surround-
ing parts. A selective concrete demolition technique to precisely remove a
specific portion with a large surface area of a concrete component without
affecting the surrounding concrete and finishes is in high demand in many
repair and retrofitting applications. An example of this is removal of the
chloride-contaminated surface of the concrete in roads, offshore and marine
structures, and underground concrete structures for replacement with a new
concrete layer without adversely affecting the underlying layer. Selective
demolition allows reusing the uncontaminated concrete, thereby extending
the service life, and has the potential to significantly improve sustainability
by preserving the embodied energy already invested in fabricating the origi-
nal concrete components that are retained.
Another area of application may involve the need to accurately remove a
specific part or portion of a concrete component. An example of such appli-
cations is in the decontamination of nuclear facilities and facilities used for
storage of hazardous materials. Decontamination is an important stage in
the decommissioning of old nuclear power plants, nuclear waste-processing
plants, and hazardous material storage facilities [8]. For instance, consider
the parts of a nuclear power plant or waste-processing plant in which the
concrete surface is exposed to radioactive radiation throughout their ser-
vice life. As a consequence of long-term exposure, various radionuclides
diffuse into the concrete, contaminating the surface layer. The thickness of
the contaminated layer depends on concrete diffusivity and the exposure
duration and is usually between 1 and 10 mm [9]. In conventional methods,
contaminated concrete components are demolished in their entirety and
disposed of as hazardous wastes, requiring costly precautions and sophis-
ticated disposal techniques. However, as contamination is generally con-
fined to the thin surface layer of the exposed concrete, the use of a selective
removal technique to remove only the contaminated surface layer can result
in considerable savings in the cost of disposal. The rest of the uncontami-
nated portions can be disposed of conventionally.
Microwave heating at higher ISM frequencies has been recommended
as a potential replacement for conventional concrete surface removal tech-
niques [10,11]. In the microwave decontamination technique, also known
as the microwave-assisted concrete removal technique, microwave heating